A typical brake transmission safety interlock (BTSI) operates to prevent a vehicle's transmission from being taken out of the park position if the service brake is not applied. The typical BTSI system includes an electromagnetic device positioned in the brake light circuit of the vehicle which is operable to immobilize the shifter linkage and inhibit movement of the linkage out of the park position unless and until the service brake is applied. BTSI systems also may further include an ignition switch interlock whereby the ignition key may not be removed from the ignition switch when the vehicle is out of park. Various systems have been proposed and utilized to achieve a combined brake interlock and ignition switch interlock function but these prior art systems have been complicated and expensive in construction. They have also been unreliable, thereby creating maintenance problems, have been difficult to install, and have tended to be noisy in operation.